Two days after climbing over $500 for the first time in its long history, shares of Apple (NASDAQ: AAPL) sputtered on Wednesday, ending the day down 11.79, or 2.3%, to 497.67.

That's not how the day started for Apple. Shares picked up where they left off from Tuesday's closing price of 509.46, rising as high as 526.29 shortly before noon. Apple shareholders no doubt were beginning to look ahead to the next milestone -- $600 a share.

Instead they were confronted with Apple's worst day on Wall Street since November 23, when shares fell 2.5% to 366.99. The number of Apple shares traded on Wednesday -- 53.76 million -- was the most in nearly 13 months.

Unlike Icarus, Apple shares didn't drown in the ocean after their rapid descent, so they'll live to make another run at $600 (assuming they surpass $500 again).

But Wednesday was a sobering reminder to Apple shareholders that their continued good fortune isn't written in stone. Or on an iPad.

Zynga update

Earlier I wrote that shares of Zynga (NASDAQ: ZNGA) plummeted nearly 16% to 12.11 Wednesday morning after reporting a fourth-quarter loss. The stock bounced back a bit from there, but later in the day things got worse as shares found a new low of 11.72 before closing at 11.80.